Silica/Poly(1,5‐dioxepan‐2‐one) Hybrid Nanoparticles by “Direct” Surface‐Initiated Polymerization

Summary: Biodegradable poly(1,5‐dioxepan‐2‐one) (PDXO) was grown directly from Si OH groups of a silica nanoparticle by surface‐initiated, ring‐opening polymerization (SI‐ROP) of 1,5‐dioxepan‐2‐one (DXO). The direct SI‐ROP of DXO was achieved by heating a mixture of Sn(Oct)₂, DXO, and the silica nanoparticles (316 nm in diameter) in anhydrous toluene. The resulting silica/PDXO hybrid nanoparticles were characterized by means of ¹H NMR spectroscopy, IR spectroscopy, thermogravimetric analysis, and field‐emission scanning electron microscopy.

The procedure for the surface‐initiated, ring‐opening polymerization of 1,5‐dioxepan‐2‐one on silica nanoparticles reported here.     

MULTIPLICITY OF SOLUTIONS AND SOURCE TERMS IN A FOURTH ORDER NONLINEAR ELLIPTIC EQUATION

0Introducti0nWeinvestigatetheexistellce0fs0lutiolls0fthef0urthordernonlillearellipticb0undaryvalueproblemwhereu =max{u,0},sisreal,andcisn0taneigenvalue0f-A11llderDirichletb0undarycondition.Hereweassumethatflisab0unded0pensetinR"withsmootl1b0undaryOn.The0perat0rA2denotesthebihalm0nic0perat0r.Weassumethatbisllotancigenvalue0fAa cAunderDirichletb0undaryc0llditi0n.Theno11lillcarequati0uwithjumpillgn0l1lillearityhavebeenextcllsivclystudi(}dbymany.uth.rs[3'4'6'7'8].Theyst11dicdtheexistence()fs0l…     

Electrodiffusion of ions inside living cells

Electrodiffusion of ions, both inside and outside biologicalcells, are of utmost importance to proper cellular functions.Experiments indicate that both ion concentrations and electropotentialcan jump discontinuously across the cell membranes. We studya system of nonlinear partial differential equations modellingsuch phenomena. Jump conditions for species concentrations andelectropotential across cell membranes are imposed. Under zero-fluxboundary conditions for one-dimensional domains, the solutionsare proved to exist for all times. With further assumptions,these transient solutions will converge to the unique steady-statesolution. Numerical experiments in one- and two-dimensionaldomains are also performed in order to study some unresolvedtheoretical issues.     

Capillary Electrophoresis Coupled On-Line with Inductively Coupled Plasma Atomic Emission Spectrometry for Elemental Speciation

Capillary electrophoresis (CE) has become a powerful analytical technique for the separation of a variety of analytes ranging from small inorganic ions to large biomolecules such as proteins and nucleic acids. A selective and sensitive detector for CE has been one of the most important and challenging prerequisites for the growth of CE. On-column UV-Vis detectors are commonly used to determine the analytes separated by CE. However, these detectors are often not very selective. Other detection techniques such as mass spectrometry, laser induced fluorescence, amperometry, and inductively coupled plasma spectrometry have been investigated to provide a more sensitive and selective detection for the target analytes. However, relatively few studies have been published on the use of inductively coupled plasma atomic emission spectrometry (ICP-AES) as a means of detection in CE separation.     

Delayed bifurcations and negative hysteresis in semiconductor lasers: the role of initial conditions

The dynamical intensity response of a semiconductor laser under the influence of injection current modulation, and the resulting hysteresis behavior, is investigated experimentally and theoretically. We report the first experimental observation, in a semiconductor laser, of the transition from a negative to a positive hysteresis as the modulation frequency of the injection current is varied. The theoretical work isolates the initial conditions on the intrinsic laser parameters as the sole determinant in influencing the kind of hysteresis one observes.     

A Single-Ridged Coaxial Hybrid TE011 Coupler with High Mode Purity

We design a single-ridged coaxial hybrid coupler which excites a TE₀₁₁ mode of high mode content in a cylindrical cavity, resonating at 28.2GHz. The coupler consists of a WR-28 rectangular waveguide, a coaxial TE_n11 cavity, and a cylindrical TE₀₁₁ cavity. Both TE₃₁₁ coaxial cavity and TE₄₁₁ single-ridged coaxial cavity are analyzed to examine the TE₀₁₁ mode purity in the central cavity. Mode purity analysis is performed by a field expansion method using Fourier-Bessel orthonormal basis functions. Numerical calculations predict that the TE₄₁₁ single-ridged coaxial cavity excites the TE₀₁₁ mode with mode purity of 98.6%, which is improved by 3% higher compared with the TE₃₁₁ coaxial cavity. Measurements on the single-ridged coaxial coupler show a resonant frequency at 28.078GHz and ohmic and external Qs of 1560, 473 respectively, which are in good agreement with the simulated results of a 3-D finite element electromagnetic code.     

Asymmetric borane reduction of prochiral ketones catalyzed by phosphinamides prepared from L‐serine

Synthesis of several new chiral phosphinamide catalysts with a proximal hydroxyl group from L ‐serine was described. These compounds have been successfully used in the asymmetric catalytic borane reduction of prochiral ketones. The optically active secondary alcohols were obtained with an enantiomeric excess (ee) up to 81% and excellent yields. © 2003 Wiley Periodicals, Inc. Heteroatom Chem 14:288–291, 2003; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/hc.10145     

FT‐IR and Isotherm Study on Anion Adsorption onto Novel Chelating Fibers

A new chelating fiber, poly(acrylo‐amidino diethylenediamine), was synthesized based on polyacrylonitrile fibers in diethylenetriamine with the aid of AlCl₃. Complex formation with CrO₄^2– was strongly pH‐dependent, as complexes formed only in the presence of NH₃⁺ and NH₂⁺. In the medium pH region, both ionic and hydrogen bonds were formed between poly(acrylo‐amidino diethylenediamine) and the chromate ion, as was confirmed by means of FT‐IR spectroscopy.     

New Transformation of 1,3‐Oxathiolane‐2‐thione into 1,3‐Dithiolan‐2‐one via Polymerization and Depolymerization

This article deals with the cationic and anionic depolymerization of polydithiocarbonate, which was synthesized by cationic polymerization of 5‐phenoxymethyl‐1,3‐oxathiolane‐2‐thione ( 1 ) using methyl triflate as the initiator. The cationic depolymerization of the obtained polymer was carried out in the presence of 5–20 mol‐% of methyl triflate or triflic acid catalyst in chlorobenzene at 60 °C for 96 h to afford 4‐phenoxymethyl‐1,3‐dithiolan‐2‐one ( 2 ) in 35–83% yield. The anionic depolymerization of the polymer was carried out in the presence of 5 mol‐% of triethylamine or potassium tert‐butoxide at 20 °C for 24 h to afford 2 in 85–100% yield.